How Can I Simulate Negative Lookbehind Assertions in Go?

Simulating Negative Lookbehind Assertions in Go

While negative lookbehind assertions are not natively supported in Go, there are alternative methods to achieve similar results. For instance, when attempting to extract commands like "foo bar baz" while excluding those with prefixes like "@", "#", or "/", one can utilize a negated character set instead of a negative lookbehind.

For example, the following regex matches words that do not begin with these characters:

\b[^@#/]\w.*

If characters can also appear at the start of the string, the ^ anchor can be used:

(?:^|[^@#\/])\b\w.*

Another approach involves utilizing a filter function to remove unwanted words:

func Filter(vs []string, f func(string) bool) []string {
    vsf := make([]string, 0)
    for _, v := range vs {
        if f(v) {
            vsf = append(vsf, v)
        }
    }
    return vsf
}

This filter can then be combined with a processing function to remove words with specific prefixes, as demonstrated below:

func Process(inp string) string {
    t := strings.Split(inp, " ")
    t = Filter(t, func(x string) bool {
        return strings.Index(x, "#") != 0 &&
            strings.Index(x, "@") != 0 &&
            strings.Index(x, "/") != 0
    })
    return strings.Join(t, " ")
}

By applying these filtering techniques, one can simulate negative lookbehind behavior in Go, enabling efficient matching and extraction of specific patterns.

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